1. Field of the Invention
The present invention relates generally to wireless communication, and more particularly to a method and apparatus for simulating the performance of a wireless environment by a wire environment between base transceiver stations (BTSs) of a digital cellular system/personal communication services system.
2. Description of the Related Art
A characteristic of prior art cellular systems is that handoffs inevitably occur because of frequency re-use. Also, in a code division multiple access (CDMA) system based on reuse of frequency according to pseudo noise (PN) so that handoff occurs more frequently. Therefore, stable embodiment of handoffs in a cellular system is a primary concern in the development of a mobile communication system.
A conventional handoff test which is commonly applied in the development of a base transceiver station (BTS) operates by constructing a test cell, which is dedicated to handoff. A tester moves between cells simulating an actual subscriber of a mobile communication system. Obtaining a reliable measure of an exact handoff through the aforementioned handoff test method is difficult due to the changing cell environment. Additionally, the method is deficient in that it requires considerable labor, time and capital investment.
A method is disclosed in U.S. Pat. No., 5,465,393 entitled Simulated Air Interface System for Simulating Radio Communication, the method is disclosed for an air interface simulation between base transceiver stations (BTSS) and mobile stations in a radio communication system. The air interface includes a directional coupler for splitting a radio path between a mobile station and base transceiver station, a plurality of dividers, a plurality of combiners and a plurality of generators. Also, for control of the generators, a plurality of computers are provided.
According to the above prior art, a reliable handoff simulation is impossible in a restricted room (i.e., laboratory). There exists a need, therefore, for a stable system with good quality and software and hardware need to be continuously developed.
It is therefore an object of the present invention to provide a method and system for an air interface simulation to enable early completion of the development of a cellular system by providing a rapid and consistent handoff and field environment in a laboratory setting.
It is an another object of the present invention to reduce unnecessary capital investment, time and labor on a cell dedicated exclusively to handoff testing.
According to one embodiment of the present invention, an air interface simulator comprises a first plurality of variable attenuators for equally providing a mobile station with a transmission signal received from a base transceiver station (BTS) before the air interface simulator starts driving, a plurality of attenuators for generating path loss to prevent power of the mobile station from being excessively inputted to the BTS and to construct an air environment, a first plurality of 2-way dividers for generating an input terminal for providing load in a reverse link of the BTS and combining the provided load and a RF signal of the mobile station, a plurality of duplexers for duplexing a transmission signal and a received signal of the BTS into a RF signal of the mobile station, a second plurality of variable attenuators for generating path loss and long-term effect, the second plurality of variable attenuators being connected to said plurality of duplexers, respectively, a first plurality of 4-way dividers for combing input signals from each BTS, a second plurality of 4-way dividers for combining input signals from each mobile station, transmitting the combined signal to the first plurality of 4-way dividers and a decoder circuit for controlling the first and second plurality of variable attenuators, the decoder circuit being provided with control input from a parallel port of a control computer.
According to another embodiment of the present invention, a method for air interface simulation in a forward link, comprises the steps of providing a transmission signal of each base transceiver station (BTS) to a first variable attenuator, transmitting an output of the first variable attenuator to a duplexer, attenuating an output of the duplexer at a second variable attenuator and combining the attenuated signal through a 4-way divider after the attenuation and dividing again the combined signal again to each mobile station.
According to another embodiment of the present invention, a method for air interface simulation in a forward link, comprises the steps of providing a radio frequency (RF) signal of a mobile station to a 4-way divider, dividing the RF signal into the same level wherein the RF signal is provided to the 4-way divider, attenuating the divided RF signals by a variable attenuator, providing the attenuated RF signals to a duplexer, combining the output signal of the duplexer with an addictive white gaussian noise (AWGN) signal, providing the combined signal to an attenuator, dividing output signal of the attenuator into 2 paths using 2 WD and providing the divided value to an input port of the base transceiver station.
The present invention advantageously streamlines the development of a cellular system more quickly via a simulation method. The present invention can assess whether a proposed cellular system will operate well in a real air environment, thereby saving time and expense in system development.